1. Field of the Invention
The present invention relates to a rotary table.
2. Description of the Related Art
A rotary table is, for example, mounted in a machine tool that is controlled by a numerical controller, and is used to secure a workpiece, a jig, and the like on a rotating portion of the rotary table for indexing, rotation supporting, and other purposes.
Such a rotary table is arranged with a clamping mechanism that takes a more important role than other components of the rotary table because how quickly this clamping mechanism operates affects a cycle time for processing a workpiece with a machine tool, i.e. such a clamping mechanism is directly linked to the processing capability.
An indexing rotary table or a rotary table supporting a cradle type rotary jig, which is arranged in a numerically controlled (NC) machine tool, usually has a built-in clamping mechanism that operates pneumatically, hydraulically, or other means. Such a built-in clamping mechanism is normally provided with a biasing mechanism for biasing the clamping mechanism in a clamping or unclamping direction when no power, such as pneumatic or hydraulic power, is supplied.
A method using a coil spring, which method is disclosed in JP 4732734 B2, is widely applied in such a biasing mechanism arranged in a rotary table because the method is advantageous for a compact-sized device since such a coil spring does not require a larger space for installation. However, such a method requires more operating fluid to fill a space for accommodating the coil spring, which could lead to reduced responsiveness in a clamping mechanism. Moreover, such a method using a coil spring is also disadvantageous because the method makes difficult to apply a function for preventing a piston from being rotated, in addition to insufficient clamping torque.
In JP 5057568 B2, to solve these problems, rotation stopping and biasing functions, which were difficult to achieve in a piston-structured clamping mechanism, are achieved through a structure in which a brake disc is clamped with a spring member without using a piston method in a normally-clamping type indexing rotary table. However, since the structure disclosed in JP 5057568 B2 basically uses a spring member for either clamping or unclamping, it is difficult to pneumatically drive the structure for both clamping and unclamping operations, unlike a typical piston structure.
JP 5468581 B2 discloses a brake structure for a rotary table, in which structure an elastically deformable clamping member is used for selecting a clamped or unclamped state while operating fluid is supplied, or a clamped state while operating fluid is not supplied. However, in the structure disclosed in JP 5468581 B2, because a piston does not face a pressure chamber as can be seen in a piston structure, a pneumatic path might be complicated, thus the operating speed could be affected.